1. Field of the Invention
The present invention relates to micromachining of a substrate, and more particularly, to a material for use in forming a fine pattern on a substrate and a method of forming a fine pattern using the material.
2. Description of the Related Art
Intensive research on fine patterning methods, such as photolithography, using vacuum ultraviolet rays (VUV) or X-rays, which are applied in the manufacture of semiconductor integrated circuits or electronic/electrical parts, including optical discs, has been conducted. Fine pattern structures with a line width of 0.1 μm can be realized in current situations based on such patterning techniques, and their commercialization is expected in a few years.
A conventional method of forming a resist pattern in the manufacture of electronic/electrical parts involves irradiating with activation light a photoresist layer through a predetermined mask pattern and developing the photoresist layer. Accordingly, the dimensions of the resist pattern are limited to be slightly smaller than the wavelength of the activation light used, due to diffraction of the activation light. The diffraction limit depends on the wavelength of light and the numerical aperture of a lens used. Shorter light wavelength and greater numerical aperture of a lens are more effective in reducing the diffraction limit. However, since increasing the numerical aperture of the lens has limitations, there are more trends toward using a shorter light wavelength to form smaller resist patterns.
New exposure technology using deep UV, laser light, or soft X-ray has been researched. Currently, it is possible to form a fine pattern of about 150 nm in size using a KrF eximer laser or an ArF eximer laser. However, there are needs for improvements in these techniques, for example, in the development of high-performance light sources, or property improvements of optical materials or resist materials. Furthermore, there are also needs for technology improvements that allows for the use of smaller light sources or optical systems and saves energy.
Electron beam lithography permits much finer pattern processing in nanometer pattern dimensions compared to photolithography. However, electron beam lithography requires an additional vacuum enclosure, a large electrode, and a high power source for electron acceleration or deflection. Also, the use of a high accelerating voltage of tens of kilovolts raises safety concerns.
In addition, using smaller wavelength of light or electron beam to form fine patterns in the above-described techniques is costly. To overcome such defects in the conventional fine pattern formation methods, various methods of forming fine patterns have been suggested. For example, Japanese Patent Application No. hei 8-249493 discloses a pattern formation method in which the crystalline state of chalcogenide is thermally changed by laser light irradiation. This fine patterning method is based on variation in etch rate between different crystalline states and ensures patterning to be smaller than the diffraction limit. However, the variation in etch rate depending on crystalline states is not large enough, and the uneven chalcogenide layer leads to varying etch rates even for the same crystalline state. Moreover, a chalcogenide layer is etched first at an intercrystalline domain so that a quality fine pattern is not guaranteed. In addition, chalcogenide, which is an essential material of the disclosure, cannot be applied to form a fine pattern for semiconductors. Other problems arise from the change of the chalcogenide.
A pattern forming material which thermally changes by activation light irradiation and a patterning method using the material are suggested (Microelectronic Engineering 61-62, 2002, p. 415-421). In this disclosure, a light-to-heat converting material layer made of Ge2Sb2Te5 is interposed between a target substrate and a photoresist layer to be patterned and is subjected to activation light irradiation to generate heat. The heat generated in the Ge2Sb2Te5 layer is transferred to the overlying photoresist layer inducing chemical reactions and forming a fine pattern therein. A pattern of 100 nm can be formed with this method. In addition, since a low cost semiconductor laser is used as an activation light source and energy consumption is small, compared to techniques which require costly high-performance light sources, such as a KrF eximer laser, or ArF eximer laser, or electron beams, the disclosed method is regarded to be very economical and offers higher processing precision and finer pattern processing ability compared to the method using chalcogenide.
However, the above resist patterning method using the light-to-heat converting material layer has the following limitations. The amount of heat transferred from the light-to-heat converting layer to the photoresist layer is not enough to form a desired fine pattern. The maximum pattern height that can be obtained with this method is limited to 30 nm when the width of a pattern is designed at 100 nm. In other words, this method cannot be applied to form a high aspect ratio pattern on a substrate. When the intensity of laser light radiated is increased to generate a larger amount of heat or for a higher processing rate or greater pattern height, the photoresist layer undesirably evaporates and disappears.